The present invention relates to a method of priming an inkjet printhead without removing the printhead from a carriage of a printer and to a printer for priming a printhead and in particular, to priming a printhead having an air chamber connected to the atmosphere via a vent by the application of a positive pressure to the vent.
The present invention relates to the art of inkjet printing mechanisms whether of the thermal or piezo variety which may be included in a variety of different products including copiers and facisimile machines in addition to standalone printers either desktop mounted, portable or freestanding. Herein a freestanding printer will be used to illustrate the present invention. Printers of this type have a printhead carriage which is mounted for reciprocal movement on the printer in a direction orthogonal to the direction of movement of the paper or other medium on which printing is to take place through the printer. The printer carriage of a color printer typically has two or more, usually four, thermal ink jet printheads mounted thereon which may be removable. Each of the printheads contains or is attached to a supply of ink and occasionally it is necessary to prime one or more printheads by creating a pressure differential to force ink to flow into the ink delivery orifices or nozzles. Such priming for maintaining or recovering the operation of the printhead is becoming increasingly important as the printheads used in inkjet printers are required to have greater lifetimes. A number of printhead problems can be solved or alleviated by performing a priming operation on the printhead, for example dry or crusting ink, air bubbles or foreign particles may be removed from a nozzle or its associated firing chamber by priming. Also a condition known as local or global deprime (dependent on the number of nozzles affected), in which the continuity of ink supplied from the ink chamber of a printhead usually via narrow conduits to the nozzles is broken, can be corrected by priming the printhead.
A related but distinct aspect of printhead lifetime which is not addressed by the present invention is the undesirable accumulation of large quantities of air within the ink chamber of a printhead, known as warehoused air.
Printhead priming has usually previously been done by positioning a compliant seal around the printhead after the printhead carriage has been parked at a service station. In these systems, ink is drawn through the printhead nozzles by applying a negative pressure to the outside of the nozzle plates of the printheads to suck ink through the orifices. The negative pressure is generally maintained by pressing a compliant cap against the surface surrounding the nozzles to create a chamber closed to the atmosphere but connected to the negative pressure source. The source of the negative air pressure differential has been, among others, a collapsing air bellows, a remote pump connected by a fluid conduit or a movable diaphragm within a priming cap as described in U.S. Pat. No. 5,714,991. The use of negative pressure applied to the nozzle plate of a printhead has a number of disadvantages such as causing ink drawn out in this manner to foam which may lead to air bubbles blocking the nozzles and is also a technique over which it is difficult to establish precise control.
It is also known to apply a positive pressure to the ink within a supply line of a printhead served by a remote ink reservoir in order to force ink under pressure into the printhead and thus to prime the printhead, for example as described in U.S. Pat. No. 4,517,577 and GB 2304639. Such priming causes a significant flow of ink into the printhead through the supply line and out of the printhead through its nozzles and has a number of disadvantages. In addition to causing excessive ink waste and requiring this waste ink to be collected and stored in the printer, such significant flows of ink under pressure are hard to control accurately and may cause damage to the structures within a printhead for example in the vicinity of the nozzle plate, particularly in more modern complex printhead designs. In order to achieve sufficient control over the pressure and volume of ink pumped under pressure into a printhead an expensive ink displacement pump is required and the printer must additionally withdraw a controlled amount of ink from the printhead to reset the necessary negative pressure within the printhead.
Additionally, it is known to purge warehoused air from within the ink chamber of a printhead having an ink regulator and an air chamber by applying a positive air pressure to the air chamber so as to drive out warehoused air via either the nozzles, the ink inlet or a gas purge vent as described in EP 0857576 and U.S. Pat. No. 5,736,992.
According to a first aspect of the present invention, there is provided a method for priming an inkjet printhead without removing the printhead from a carriage of a printer, the printhead having a body comprising an ink chamber in fluid communication with a plurality of ink ejection nozzles in a nozzle plate and a variable volume air chamber coupled to said ink chamber and having a vent which is in gaseous communication with ambient atmosphere, the method comprising the steps of moving the carriage to a service area within the printer, interfacing a source of gas to the vent of the air chamber of the printhead, and delivering a predetermined controlled volume of gas from said gas source at a pressure above ambient atmospheric pressure to the air chamber so that the air chamber expands within the printhead body causing an increase in the pressure within the ink chamber and thus a controlled flow of ink into the nozzles of the printhead to prime the printhead. It has been discovered by the present Applicant that the controlled delivery of a predetermined volume of air to the air chamber of a known design of printhead ink regulator while the printhead is mounted within the printer can be utilised to effectively prime the printhead in a manner which is highly controllable and which does not cause damage to the printhead and thus can be repeated many times during the lifetime of the printhead.
Preferably, during priming of the printhead a controlled volume of ink passes through the nozzles onto the outside of the nozzle plate and the majority of said ink is drawn back through the nozzles and into the printhead. This flowback of ink into the printhead has been found to be effective in resolving a number of problems with printheads which are difficult to resolve without such flowback of ink. Furthermore, the quantity of waste ink in greatly reduced.
Advantageously, the ink chamber comprises an ink regulator through which the ink chamber receives ink at a pressure above ambient atmospheric pressure from a remote ink reservoir and the preferred priming method controls the ink delivery pressure during priming of a printhead so that substantially no ink flows into the printhead from the ink reservoir during priming. Thus preferably the increase in pressure within the printhead which causes priming of the printhead is due substantially only to the air delivered to the printhead.
According to a second aspect of the present invention, there is provided a printer in which an inkjet printhead may be primed without removing the printhead from a carriage of the printer, the printer comprising a source of gas capable of delivering a predetermined controlled volume of gas at a pressure above ambient pressure, a carriage for holding at least one printhead and having coupling means for coupling a vent on the printhead to the source of gas, and a controller for controlling the priming of a printhead by the application of a controlled predetermined volume of gas to a printhead mounted in the carriage.
Preferably, the controller of the printer comprises storage means for storing priming data for use in priming an identified printhead.
More preferably, the stored priming data comprises data affecting at least one of the following parameters for priming the identified printhead 1) a volume of gas supplied to the printhead, 2) a duration for which a pressure above ambient is applied to a printhead, 3) a temperature to which the printhead should be heated prior to priming, or 4) an ink supply pressure of a remote ink reservoir in fluid communication with the printhead.
Most preferably, priming data is stored for a plurality of printheads and the priming data for at least two of the printheads is different.